3. You share your fundraising page online so often that everyone un-follows you on Twitter and hides you on Facebook.

4. Whenever you do interval training (short bursts of sprints mixed with gentle jogging) someone extremely attractive is always walking in front of you. This means you look at best like a man trying and failing to impress them. Or at worst like you’re considering, but then reconsidering, making some sort of sweaty pass at them.

5. You lose any spenders’ guilt and splash out on kit, gadgets, pills and gels. You even use some of them.

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6. As your alcohol tolerance level plummets to that of a teenage experimenter, you arrive at full-blown, slurred confessional stage somewhere towards the end of your second pint.

7. During an icy snap you are forced to do your training indoors on a treadmill. Just five minutes into a two-hour run you are already bored to tears.

8. You get a cold.

9. You quickly re-write your perspective on distance. A half marathon, something you’d previously spend six months preparing for, is now a distance you nonchalantly complete on Tuesday evenings. 10ks become kids stuff. 5ks? What even are they?

10. You suffer from chafing in the most inconvenient bodily zones.

11. During a long run you get all giddy and find yourself struck by an epiphany. You get home and share with your partner your new business pitch / screenplay idea / peace plan for the Middle East. They scarcely understand a word you’re saying.

12. When you get injured you are secretly thrilled. It gets you a week’s guilt-free rest and you can talk about your strain as if you were a top-flight footballer.

13. You compile a playlist of power songs to play (Eye Of The Tiger, Simply The Best etc) when you need a special psychological boost. You cross your fingers nobody finds it.

14. You get carb-loading wrong and for a day or so the only running you get done is to the toilet.

15. Weather forecasts become your new obsession. There is no weather app you don’t download.

16. You become familiar with the defence mechanisms of overweight non-runners. "I heard it destroys your knees; 26 miles just seems unnatural; rather you than me…" Don’t worry, they waddle off in the end.

17. At least once a fortnight, some wag shouts: “Run, Forrest, run” at you.

18. Exhausted all the time, you leave social gatherings as early as politeness permits. You start to prefer quiet nights in, watching TV. You generally fall asleep in front of the box somewhere around 8pm.

19. You get another cold.

20. You start your Sunday morning runs so early that you encounter revellers still out from the night before. You were that guy once.

21. You get lost during runs, discovering hidden parts of your neighbourhood and feeling like Christopher Columbus.

22. As your training programme nears its peak, to your horror you realise that you’re actually putting on weight. Thanks to an increase in muscle mass and glycogen storage, plus your tendency to crash out after a long run, you begin to gain, rather than lose, pounds.

23. You do, however, lose at least one toenail.

24. You keep yourself motivated by imagining yourself on race day, striding triumphantly towards the finish line, as your proud friends and family cheer you on from the side. (None of them will turn up on the day.)

25. With three weeks to go, you taper - drastically reducing your weekly mileage. Even though this is recommended by almost every expert in the world, it feels so wrong.

26. Finally, you reach the end of your exhausting, bewildering training programme. Pat yourself on the back – you did it! Now you just have the small matter of the 26.2 miles to complete…